1. Field of the Invention
The present invention relates to an ink-jet printing apparatus and a method for controlling thereof. More specifically, the present invention relates to wiping a surface (hereinafter referred to as the ejection opening formed face), on which ejection openings for ejecting ink in a printing head is formed, with a wiper to thereby maintain ejection performance.
2. Description of the Related Art
Printing apparatuses having functions as a printer, a copying machine, a facsimile, and the like, and printing apparatuses used as output equipment for complex electronic equipment including a computer and a word processor, a workstation, or the like is known. Such printing apparatuses are intended for use in printing images (including letters and symbols) onto a printing medium such as paper, cloth, a plastic sheet, or an OHP (overhead projector) sheet based on printing information. Among them, an ink-jet printing apparatus is intended for use in performing printing by ejecting ink onto a printing medium from a printing head. In this type of apparatus, the printing head is easily made compact, a high-resolution image can be printed at high speed, and printing can be performed onto plain paper without requiring special handling. This type of apparatus also has various other advantages such as a low running cost, low noise because of being a non-impact type, and easy printing of color images with the use of a wide variety of inks.
As an element for generating the energy to eject ink in a printing head, there exists an element that uses an electromechanical conversion element such as a piezo element, that utilizes the heat generation caused by irradiation of an electromagnetic wave such as a laser leading to the heat generation, that uses an electrothermal conversion element with a heat element, and the like. Among them, a printing head that uses the electrothermal conversion element can perform high-resolution printing because the ejection openings can be arrayed very densely. Also, the printing head using the electrothermal conversion element can be more easily made compact than the others; sufficiently utilize technological advances in the recent semiconductor field, the advantages of IC and micro process technologies of which reliability is significantly high; and this leads to high-density packaging more easily and lower manufacturing costs.
Furthermore, for various requirements for materials used as printing media, not only paper (including thin paper and treated paper), which is an ordinary printing medium, and a thin resin sheet (OHP, etc.), but also cloth, leather, non-woven cloth, even metal, and the like can be used as the printing media.
The above-described printing apparatuses can be roughly divided into a serial-type printing apparatus in which printing is performed while scanning is performed in a direction intersecting that of the conveying direction of the printing medium, and a full-line type printing apparatus in which a printing head arrayed with ejection openings according to a range in a width direction of the printing paper is held, and the printing medium is conveyed relative to the printing head to thereby perform printing. With the serial-type printing apparatus, an image is formed over the entire printing medium by repeated main scanning for printing the image with a printing head mounted on a carriage moving along the printing medium and conveying of a predetermined amount of paper (sub-scanning), after the printing medium is supplied to the predetermined printing position.
Meanwhile, with ink-jet printing apparatus, foreign matters such as ink droplets, dirt, dust, and paper powder may be attached to the surface of the printing head with a printing operation, and in order to remove such foreign matters, wiping (for example, wiping by rubbing) is performed. As a wiper (wiping member) used for the wiping, a flexible member such as a rubber blade made of a rubber-like elastic material is usually used. Also, ink near the ejection opening of the printing head may dry, causing clogging of the ejection opening due to thickening, fixing, or deposition of the ink. Further, the clogging of the ejection opening may occur due to air bubbles generated inside the ejection opening (liquid path), dust, or the like. As a system for recovering (preventing, eliminating, etc.) such clogging, a suction recovery operation is performed. That is, using a capping member to thereby form a closed system between the ejection opening formed face of the printing head and the member, and using a pump to thereby generate suction with negative pressure in the closed system cause the ink to be forcibly discharged from the ejection opening. Then, after the suction recovery operation has been performed, also the above-described wiping is performed. This can remove any ink attached to the ejection opening formed face due to the capping or the like.
Further, as the ink used in ink-jet printing apparatus, the use of aqueous dye ink had been mainstream. However, the dye ink does not adequately ensure so-called weather resistance such as resistance to light and gas because the molecules of the dye are very small, and therefore the problem of temporal color deterioration of the printed matter has existed, among others. For this reason, in recent years, aqueous pigment ink has been in practical use rather than the aqueous dye ink. The pigment ink being used now has a particle size of approximately 100 nm, which is considerably larger than the size of the dye molecules, so that even if it is affected by light or ozone, color deterioration of the color material is not significant, and the weather resistance of it is considerably better when compared with the dye ink.
However, with ink-jet printing head using such pigment ink, a problem may arise that is not significantly seen in an apparatus using the dye ink, regarding the wiping. That is, with the pigment ink, the period of time before thickening or fixing of the ink is shorter than in the case of the use where dye ink is used. Also, a cleaning-ability performed by scraping (or wiping) the pigment ink with the wiping member is lower than in the case where dye ink is used. For this reason, even if the ejection opening formed face of the printing head is wiped, the wiping may cause a thin film of the pigment ink to be formed on the ejection opening formed face, and furthermore the ink fixes in place, causing the problem that the effect of the wiping is of little use.
The pigment ink is ink in which hydrophilicity is given to pigment particles by pigment dispersions to thereby disperse them, or terminals of a structure itself of each of the pigment particles are made to have hydrophilic groups to thereby make them self-disperse in an aqueous solution, because the pigment particles are not generally dissolved in water. Accordingly, the ejection opening formed face gets wet easily with the pigment ink when the pigment ink is ejected from the printing head. Also, in the case of the ink using the dispersion materials such as resin, the resin easily wet the ejection opening formed face along with the pigment. Furthermore, performing the wiping while the pigment particles are present on the ejection opening formed face causes damage (such as scrapes) to the ejection opening formed face, which is also one of contributing factors causing the ejection opening formed face to get wet easily. Then, such wetting on the ejection opening formed face due to the pigment ink is nonuniformly formed, and the nonuniform wetting affects the ejected ink, causing defective ejection such as instability of an ejection direction.
For such a problem, there can be considered the use of a printing head in which a so-called water repellent treatment for repelling the pigment ink is given to the ejection opening formed face of the printing head. However, in the beginning of the use of the printing head, the problem such as the instability of the ejection direction does not arise, but if easily wetting ink such as the pigment ink is used, the water repellency is gradually deteriorated, resulting in the loss of the effect such as the stabilization of the ejection direction. The wiping also results in the spread of the easily wetting pigment ink on the ejection opening formed face, so that the water repellency becomes deteriorated.
Regarding the above problem, Japanese Patent Laid-Open No. 11-334074 (1999) describes that the periphery of the ejection opening of the printing head is made hydrophilic, which causes uniform wetting by the pigment ink, resulting in the prevention of the deviation in the ejection direction and the like due to nonuniform wetting. However, the effect of the hydrophilic treatment of the ejection opening formed face cannot be maintained for a long time, similarly to the water repellent treatment, but is deteriorated with time. Even if a relatively well-known UV ozone treatment or the like is given, the hydrophilic level is varied with time although hydrophilicity is exhibited immediately after the treatment.
Regarding the problem of such a variation in water repellent performance or hydrophilic performance on the ejection opening formed face, for example, Japanese Patent Laid-Open No. 10-138502 (1998) describes a technology of so-called wet wiping. This is a technology in which an extremely low volatile solvent (hereinafter referred to as a wetting liquid) such as glycerin or polyethylene glycol is attached to a wiper for wiping the ejection opening formed face, and the ejection opening formed face is wiped with the wiper to which the wetting liquid is attached. This can prevent wettability of the ejection opening formed face from varying. That is, functions of the use of the wiper to which the wetting liquid is attached is firstly to dissolve thickened matters of ink and matters with increased film layers accumulated on the ejection opening formed face. Secondly, it is to serve as a lubricant by intervening between the wiper and the ejection opening formed face. Thirdly, it is to attach the wetting liquid on the ejection opening formed face to thereby form a film for protecting the ejection opening formed face.
One example of a system for wet wiping is as follows. Principally, a wetting liquid holding portion for holding the wetting liquid is provided within a moving range of the wiper. The holding portion holds the wetting liquid, and the wiper comes into contact with a transfer portion provided in the holding portion, whereby the wetting liquid can be transferred to the wiper. The wiper comes into contact with a member for cleaning the wiper along with the movement of the wiper, and thereby the wiper is cleaned. After the cleaning, the wiper moves in the same direction and then comes into contact with the transfer portion in the wetting liquid holding portion. This allows the wetting liquid to be transferred to the wiper. Subsequently, the wiper returns to an original position, and then wipes the ejection opening formed face of the printing head with the part of the wiper to which the wetting liquid has been transferred while moving in the same direction as above.
However, the conventional system of wet wiping has some problems caused by the decrease in remaining amount of the wetting liquid in the wetting liquid holding portion.
A first problem is that with decreasing the remaining amount of the wetting liquid, a transfer amount to the wiper is also decreases.
FIG. 1 is a view schematically illustrating an appearance of transferring of the wetting liquid. In the figure, the reference numerals 10 and 21a denote the wiper, and the transfer portion formed of an absorber, foam, or the like in the wetting liquid tank, respectively. The wetting liquid holding portion or the transfer portion 21a has a large number of pores, and the wetting liquid forms menisci in the pores. When the wiper 10 comes into contact with the transfer portion in this state, the menisci are broken at a contact portion and the wetting liquid wets a surface of the wiper. At this time, if a remaining amount of the wetting liquid is large, the menisci are likely to be broken because force to form a meniscus in each of the pores is low, and even after the menisci have been broken, the menisci do not much move back into the pores. Accordingly, speed of wetting the wiper with the wetting liquid is high, resulting in a large transfer amount to the wiper. In contrast, if the remaining amount of the wetting liquid is relatively small, the menisci are unlikely to be broken because the force to form a meniscus in each of the pores is high, and after the menisci have been broken, the menisci move back. Accordingly, the speed of wetting the wiper is low, resulting in a small transfer amount to the wiper. In this manner, with decreasing the remaining amount of the wetting liquid, the transfer amount to the wiper decreases. As a result, the effect of the wiping is not sufficiently performed, which may cause an ejection failure.
Furthermore, if such an insufficient transfer state becomes extreme, there may be a so-called dry wiping state in which the wiping is performed without any wetting liquid on the wiper. If this state lasts long, water repellency on the ejection opening formed face of the printing head is significantly deteriorated and therefore the ejection direction becomes unstable, which causes an increase in the variation of landing position, whereby the image deterioration becomes significant. Also, for example, a user using the apparatus may repeat cleaning unnecessarily without understanding the cause of the image deterioration, causing an adverse effect of unnecessary consumption of ink. Accordingly, the apparatus becomes inconvenient to the user.
For the above-described extreme decrease in the remaining amount, the wetting liquid holding portion usually has a capacity capable of holding a coating liquid in an amount assumed for a maximum number of sheets in terms of durability (an apparatus lifetime converted into the number of printed sheets; hereinafter referred to as a number of sheets on durability) of the ink-jet printing apparatus. On the other hand, the capacity of the wetting liquid holding portion greatly affects a size and a cost of the printing apparatus. For this reason, the capacity of the wetting liquid holding portion is generally estimated from a total usage of the wetting liquid that is calculated based on an assumption that the user uses the apparatus in an ordinary usage pattern for the number of sheets on durability. In this case, if the user continues to use the apparatus in the condition where the number of sheets on durability in the apparatus is exceeded, or if the wiping is performed more than the assumed number of times due to user's usage even in the case that the number of sheets on durability is not exceeded, consumption of the wetting liquid by these wet wiping may increase, resulting in an extremely small remaining amount. The case where the wiping is performed more than the assumed number of times includes the cases of high printing duty and high printing frequency.
A second problem is that the decrease in the wetting liquid makes the printing apparatus unavailable even if there is room in other factors defined according to the number of sheets on durability.
The cumulative number of pulses to be supplied to the electrothermal conversion element in the printing head and a capacity of a waste ink absorber are the factors defined according to the number of sheets on durability in the printing apparatus, similarly to the capacity of the wetting liquid holding portion. If the use of the printing apparatus is prohibited based on the decrease in the remaining amount of the wetting liquid even if there is room in other factors as above, the apparatus becomes inconvenient to the user.
For example, a factor which first reaches a limit according to the assumed number of sheets on durability among a plurality of factors defined with the number of sheets on durability of the printing apparatus depends on as to how the user uses the apparatus. For example, if there frequently occurs a case where the user intermittently prints a small number of copies of documents (for example, a case where the user prints one sheet of text every 10 minutes), the wiping for the capping operation performed after the printing has been performed for each printing. This case corresponds to the state of a small number of printed sheets having been printed or of a low printing duty, from the beginning, i.e. the state where there is room in the cumulative number of pulses and the capacity of the waste ink absorber, and it also corresponds to the state of a small remaining amount of the wetting liquid. In this case, if it is prohibited to use the printing apparatus without notifying any information because of the small remaining amount of the wetting liquid, the apparatus becomes inconvenient to the user due to the unaccountable prohibition.